A known seat reclining apparatus for a vehicle is disclosed in JP2009-207600A (hereinafter referred to as Patent reference 1). The seat reclining apparatus disclosed in the Patent reference 1 is provided with a ratchet including a cylindrical portion formed with an internal tooth portion and a protruding face, a guide journaled at the ratchet, pawls each of which movement in a radial direction is guided by guiding walls provided at the guide, a cam engaging with the pawls, and a hinge cam connected to the cam so as to integrally rotate with the cam. A rotation of the cam causes the pawls guided by the guide (the guide walls) to advance and retract in the radial direction, thereby bringing the internal tooth portion of the ratchet and external tooth of each pawl into engagement with each other and releasing the engagement thereof. Thus, a rotation of the ratchet relative to the guide is restricted and allowed. Accordingly, a rotation of a seatback relative to a seat cushion is restricted and allowed (locked and unlocked), and the seatback may be adjusted and retained at a desired inclination angle suitable for, for example, an occupant to be seated. In addition, in a case where the pawls guided by the guide (the guide walls) are advanced in the radial direction by the rotation of the cam, the external teeth of the pawl are in contact with the protruding face of the ratchet. Thus, the rotation of the ratchet relative to the guide is unrestrictable. In other words, the pawls are arranged at three positions leaving intervals of ninety degrees thereamong, and thus an area at which no tooth is formed (the protruding face) is provided at the cylindrical portion of the ratchet, next to the internal tooth portion. Accordingly, the seat reclining apparatus disclosed in the Patent reference 1 is configured so that locking is not established in a case where the ratchet rotates and a specified pawl, from among the pawls, corresponds to or matches the area at which no tooth is formed. This is for avoiding unnecessary locking in a state where the seatback leans forward.
The cam is biased by a biasing spring for locking, which is mounted on the hinge cam for a purpose of locking so as to rotate in a direction in which the pawls are advanced in the radial direction, that is, in a direction in which the external teeth of the pawls mesh with the internal tooth portion of the ratchet or in which the external teeth of the pawl are in contact with the protruding face. The hinge cam is integrally rotatably connected to an operation shaft to which a releasing operation force is to be inputted. Accordingly, the cam is biased by the biasing spring via the hinge cam to rotate, and thus, the external teeth of the pawls are brought to, for example, mesh with the internal tooth portion of the ratchet. On the other hand, as the releasing operation force is inputted to the operation shaft, the cam rotates in an opposite direction against a biasing force of the biasing spring, and thus the cam causes, for example, the external teeth of the pawls disengage from the internal tooth portion of the ratchet.
According to the Patent reference 1, when the releasing operation is performed on the operation shaft in a state where the seatback is leaned back, that is for example, when the seatback is leaned or moved forward by the biasing force of the spring in order to stand the seatback, there is a possibility that the external teeth of the pawl collide with the area at which no tooth is formed (the protruding face), which may cause deformation of a tooth tip.
On the other hand, a known seat reclining apparatus for a vehicle is disclosed in JP2010-22401A (hereinafter referred to as Patent reference 2). According to the known seat reclining apparatus disclosed in the Patent reference 2, avoidance of the aforementioned collision of the external teeth of the pawls is suggested while an engagement structure of the pawl and the cam is different from that disclosed in the Patent reference 1. In other words, an upper arm formed with internal teeth includes a circular recessed portion arranged so as to be concentric with the internal teeth and is formed with a protruding portion provided at the circular recessed portion so as to protrude inwardly in a radial direction. A pawl formed with external teeth meshable with the internal teeth includes a step-like engaging portion provided to face an inner circumferential surface of the circular recessed portion in the radial direction. In other words, the external teeth and the engaging portion of the pawl are arranged at different positions from each other in an axial direction. As the upper arm rotates, in a case where the engaging portion of the pawl faces and is in contact with the protruding portion of the circular recessed portion in the radial direction, the external teeth of the pawl do not mesh with the internal teeth of the upper arm, and thus locking is not established. In a case where the engaging portion of the pawl is out of contact from the protruding portion of the circular recessed portion in the radial direction, the external teeth of the pawl are meshable with the internal teeth of the upper arm. Thus, the aforementioned collision of the external teeth of the pawl, which occurs for example when the seatback leans forward, may be avoided.
In a case where the structure (the circular recessed portion and the engaging portion) of the Patent reference 2 is applied to the Patent reference 1 in order to avoid the collision of the external teeth of the pawl, a clearance that corresponds to the circular recessed portion is generated in a space in which, for example, the pawls and the cam are accommodated. Thus, retention of postures of the pawls, the cam and the hinge cam may possibly be unstable in the axial direction. This is because engagement structures of the pawls and the cam (a hook and an engagement portion), in which the pawls are advanced and retracted in the radial direction as the cam rotates, are established in an identical range in the axial direction, and the engaging portion configured to face the protruding portion formed at the circular recessed portion is arranged in the circular recessed portion.
In order to fill the clearance generated in the space in which, for example, the pawls and the cam are accommodated, it may be considered that the hinge cam is extended in the axial direction corresponding to the circular recessed portion, and that a flange protruding outwardly for restricting the pawls and the cam in the axial direction is arranged at the extended portion of the hinge cam. However, in a case where the aforementioned flange is provided at the hinge cam which is supported by a guide at one side of the hinge cam (that is, a cantilever-type hinge cam) and which is biased by a biasing spring at a protruding portion protruding from the guide outwardly in the axial direction, an axis line of the hinge cam may be inclined by a biasing force of the biasing spring. In such a case, the flange may be inclined associated with the inclination of the axis line, and thus the flange may interfere with the pawl and the cam, or with the circular recessed portion of the ratchet. Accordingly, operations related to locking and unlocking (specifically, the locking operation) may not be performed smoothly.
A need thus exists for a seat reclining apparatus for a vehicle which is not susceptible to the drawback mentioned above.